Acute ischemic stroke (AIS) is a significant cause of morbidity and mortality in the United States and worldwide. Undoubtedly, the emergence of mechanical thrombectomy (MT) as a standard of care for anterior circulation large vessel occlusions (LVOs) has improved stroke outcomes. Notwithstanding, the burden of disease remains significant. Even when patients with AIS-LVO receive MT, only ~ 70% achieve successful revascularization and more than half of patients remain with moderate-to-severe disability. The problem is exacerbated by the high proportion of cryptogenic stroke in the AIS-LVO population for which effective and targeted secondary stroke prevention strategies cannot be implemented. To date, little is known about how clot biology informs stroke etiology, revascularization success, and stroke outcomes. In our preliminary work, we have leveraged access to clot tissue retrieved at MT from the middle cerebral artery (MCA) to determine whether modern cellular transcriptional profiling, i.e., single- cell RNA sequencing (scRNA-seq), can provide insight into stroke etiology and mechanisms of thromboembolism. We uncovered a surprising enrichment and diversity of immune cells within the clot including granulocytes, macrophages, T cells and natural killer (NK) cells. These cellular constituents and their transcriptional signatures differed by stroke etiology. We also found low- abundance cardiac endothelial cells in the embolized clot of a patient with cryptogenic stroke, a powerful indicator of the embolic source. Finally, our data suggested a role for neutrophil extracellular traps (NETs) in clot biology, an emerging determinant of recanalization success. Given these findings, we hypothesize that the cellular and transcriptional profiles revealed by scRNA-seq of clots retrieved at MT will point to stroke etiology, correlate with revascularization success and patient outcomes, and uncover basic mechanisms of thromboembolism relevant to stroke pathophysiology. These hypotheses will be addressed in the experiments of the following Specific Aims: (1) to determine whether the complexity of cellular diversity in clot retrieved at MT and their molecular alterations differentiate between stroke etiologies; and (2) to determine whether transcriptional profiles of clots retrieved at MT inform revascularization success and patient outcomes. The insights gleaned from the proposed studies have the potential to be rapidly translated to the bedside, especially as it relates to an accurate determination of stroke etiology and biological basis for revascularization success.
These exploratory studies are relevant to public health for two reasons. First, they may provide proof-of-concept evidence that clot tissue retrieved during mechanical thrombectomy for acute ischemic stroke (AIS) can serve as an ?endovascular biopsy? to determine stroke etiology and better inform secondary stroke prevention strategies. Secondly, they may uncover important mechanisms important to revascularization success and stroke outcomes.
